Hydraulic system



Feb. 23, 1965 Filed June 23, 1961 2 Sheets-Sheet 1 rs S h. W U N u w 'n 5 n w i\ www j n A\ W m l W ha r1 u; 94 H W El] INVEN'roRs V u m avv/va K/.vA/A/LA/e, \n\ j [E BY g M ATTORNEYS Feb. 23, 1965 M. L.. KENT ErAL HYDRAULIC SYSTEM 2 Sheets-Sheet 2 Filed June 25. 17961 ATroRNEYs United States Patent 3,170,450 HYDRAULIC SYSTEM Melvin L. Kent, East Cleveland, Ohio, and Edward V. Manning, Watertown, NSY., assignors to rEhe New York Air Brake Company, a corporation of New .l'ersey Filed .tune 23, 1961, Ser. No. 119,170 Ciairns. (Cl. 12S- 179) This invention relates to a hydraulic system for starting internal combustion engines.

It is known in the prior art to start internal combustion vehicle propulsion engines by theuse of fixed displacement hydraulic motors. These motors are driven by pressure duid supplied from a source, such as a pump, and in order to provide suiiicient initial starting torque, large motors having a relatively high capacity are required. Such starting systems using xed displacement hydraulic motors are rather inefficient in operation since it is diiiicult to match the torque characteristics of the motors with the starting torque characteristics of the internal combustion engines with which they are used. Although control means have been proposed for controlling the pressure of the fluid supplied to the motor to cause motor operation to approximate the torque requirements of the engine during starting, these control means are complex and expensive and tend to reduce the reliability of the equipment. Furthermore, multi-ratio gear trains with speed-changing means are often required to achieve satisfactory starting operation in systems utilizing fixed displacement motors.

The object of the present invention is to provide an improved hydraulic starting system utilizing a variable displacement hydraulic motor-pump unit which is driven as a motor by uid supplied by a constant pressure source. The invention is characterized in that the rate of the fluid supplied by the source is less than the demand of the hydraulic unit at a predetermined speed less than starter cut-out speed. Pressure-responsive displacement control means are provided which maintain the motor torque constant at full rated value during an initial ignition period of the starting cycle (for example, until light-olf occurs in the starting of a jet engine) and which, after this initial period, make use of the inadequacy of the source to automatically reduce displacement as the motor continues to accelerate the starter cut-out speed. In this manner, the torque curve of the hydraulic motor is caused to correspond rather closely with the starting characteristie of the internal combustion engine with the result that the size and weight of the motor is reduced, hydraulic power for driving the motor is conserved, and the need for an unusually large source of starting fluid and complicated gear trains is eliminated.

According to the preferred embodiment of the invention, the hydraulic motor-pump unit is of the rotary cylinder barrel longitudinally reciprocating piston overeenter type operable alternately either as a motor or as a pump. The unit includes a displacement control member movable between maximum Vstroke-establishing motoring and pumping positions on opposite sides of a zero strokeestablishing neutral position. The unit is designed to be driven asa variable displacement pump by the internal combustion engine after the latter is started and obtains independent operation. By causing the hydraulic starting unit to operate as a pump, the need for auxiliary pumping apparatus for supplying pressure fluid to auxiliary hydraulic loads of the vehicle is eliminated and the weight of the vehicle yisreduced correspondingly.

As a safety feature of the invention,'selectively operable stop lmeans are provided for preventing the displacement control member from moving from its neutral position toward its maximum displacement-establishing motoring position when the hydraulic unit is being driven as a pump fmnce by the internal combustion engine. These stop means prevent reversal of the pressure relationship between the two ports of the hydraulic unit.

The pressure-responsive displacement control means serve to vary displacement of the hydraulic unit during both the motoring and pumping operations. In the preferred embodiment of the invention, the pressure-responsive means include a dual-setting pilot valve which selectively establishes two reference pressure values against which the pressure at the high pressure port of the unit is compared. The lower of the reference pressure values is utilized to control hydraulic unit displacement during motoring and low pressure pumping operation, and the higher reference pressure value is utilized to control engine displacement during high pressure pumping operation. i

Other objects and advantages of the present invention will become apparent from a study of the following specication when considered in conjunction with the accompanying drawings, in which:

FIG. l is a partly-sectioned elevational view of the hydraulic motor-pump unit used in the starting system of the present invention, the displacement control member being illustrated in its maximum stroke-establishing pumping position.

FIG. 2 is a schematic diagram of the hydraulic starting system, the displacement control member being illustrated in its maximum stroke-establishing motoring position.

Referring first to FG. l, the hydraulic motor-pump unit 3 is of the overcenter type operable alternately either as a motor or as a pump and includes a rotary group of elements consisting of a cylinder barrel having longitudinal bores therein and reciprocatory pistons mounted in said bores, said rotary group being mounted for rotation relatively to an anguiarly adjustable cam plate suspended in the unit housing. One type of such a hydraulic unit is disclosed in detail in the copending application of Tadeusz Budzich and Edward V. Manning, Serial No. 789,996, led January 29, 1959, and entitled Overeenter Hydraulic Starter Pump.

The hydraulic unit 3 comprises a housing 4 having a drive shaft 5 journalled therein to which is connected the rotary cylinder barrel 6. The rotary cylinder barrel 6 is in contiguous engagement at one end with the adjacent end face of stationary Valve plate 7, which face contains radially-arranged arcuate high and low pressure ports in communication, respectively (through internal housing passages, not shown), with the housing high and low pressure outlet ports 8, 9 (FlG. 2) which extend in opposite radial directions from the right-hand extremity of the housing 4.

rl`he cylinder barrel 6 contains a circumferential series of through longitudinal cylinder bores 11 which are arranged to register sequentially with the arcuate ports in the valve plate as the cylinder barrel rotates. Pistons 12, formed with spherical heads 13 for connection with supporting shoesV 14, are mounted in the cylinder bores for reciprocation by cam plate 15 and return plate 16.

The cam plate 15 is supported in housing 4 by cam y plate yoke portions 15a and fixed housing trunnions 17 (FIG. 2) for pivotal movement about a horizontal axis Y normal to and intersecting the axis of drive shaft 5. The

angular position ot cam vplate 1S determines the length of the strokes of pistons 12, and the cam plate is free to move between a maximum stroke-establishing motoring position (FIG. 2) and a maximum stroke-establishing pumping position (FIG. 1) located on opposite sides of a zero stroke-establishing neutral position (illustrated byv the phantom lines in FlG. 2).

Spring means 19 are provided for biasing the cam plate 15 in the clockwise direction toward its maximum spherical element 23 adapted to continuously engage cam plate 15. Preloaded spring 24, mounted concentrically about the plunger 21, reacts between the spring seat surface 25 of housing intermediate wall lb and a rigid radial liange portion 21!) of the plunger to urge the same to the right to pivot the cam plate in the clockwise direction.

Positioning motor 26 is arranged on the opposite side of the cam plate 15 from the spring-biasing means 19 andserves to pivot the earn plate in the counterclockwise direction against the biasing force of spring 2d toward the maximum stroke-establishing motoring position illustrated in FlG. 2. This positioning motor comprises a cylinder 27 rigidly secured to the housing d and con taining a reciprocable piston 23. The piston is connected at one end with the cam plate 15 by the articulated connecting rod 29. Fluid is applied to the working chamber 26a of the motor through housing passage 31 to move piston 2.8 to the left in FIG. 1.

selectively-operable cam plate stop means 32 are provided for preventing cam plate 15 from being moved by the positioning motorZ from its zero stroke-establishing position toward its maximum stroke-establishing motoring position. pressure motor consisting of a cylinder 33 rigidly connected with the housing l and a piston 34 mounted for reciprocation in said cylinder. The piston 34 isprovided at one end with an axial projection Stia having a rounded end adapted to engage the cam'plate 15. Passage l35 is provided for feeding pressure iuid to the working chamber of cylinder 33 to move the piston Edito the.

left in FiG. 1. t

The drive shaft 5 is connected, through internal gear trains (not shown) in the housing, with an intermediate shaft 36 which terminates in a splined coupling 37 connected with the power shaft of internal combustion engine 38 via mechanical connection 39.

Referring now to FIG. 2, the constant pressure fluid source 41, supplying hydraulic fluid, is connected with the housing high pressure port 8 through a iirst conduit 42 containing a flow restrictor 43 and a solenoid-controlled starter shut-ofi valve $4 operable Lbetween closed and open positions. The low pressure housing port 9 is connected with sump 45. As is conventional in hydraulic units of the overcenter motor-pump type, high pressure. fluid is supplied from the source to the high pressure These `stop means comprise a fluid housing bore is the spring seat 59. Preloaded spring dii, reacting between spring seat 59 and plunger S2, urges the seat toward` a first position in which it abuts housing wall projection 61, and urges the plunger 52 in the opposite direction into engagement with the other bore end wall to eiiect venting of the working chamber 25a of positioning motor 26 via conduit 4gb, passage-49, groove 57, passage Sti and conduit-` 51. Thepspring chamber $32. is in continuous communication with motor passage 49 via the plunger longitudinal and radial passages 53 and 6e, respectively. g. Y

For high pressure pumping operation of the hydraulic unit 3, spring seat 59 is displaced longitudinally, to a second position in'which it abuts stop 65 to increase port 8 during motoring operation, and', during pumping operation, high pressure fiuid is discharged from this same port.

'The hydraulic starting system includes a dual-setting pressure-responsive pilot valve 46 which controls the operation of the positioning motor 25. The structure and operation of one embodiment'of such a valve has been illustrated and described in detail in the Budzich et al. U.S. patent application Serial No. 789,996, ,filedv January 29, 1959, referred to above. This pilot valve includes a housing having an inlet passage 47 connected with first conduit 42 via conduit 48a, a motor passage 49 connected with the working chamber 26u of position-v ing motor 26 via conduit 48h (which includespassage 31 of FIG. 1), and an exhaustpassage Sil connected with sump 45 via conduit 51. fThe pilot valve housing includes a longitudinal boreinone end of which is mounted for reciprocation the movable valve plunger 52 having lands 55, 54 and 55 separated by grooves 5d and 57, respectively, for controlling the communication between the various valvefhousing passages. Through longitudinal slots 58 are provided in the outer periphery of land 53.

Mounted for reciprocation in the other end of the valve the preloading ofV spring and thereby establish a second reference pressure-establishing condition or operation of the pilot valve d6. This shift of the seat'59`is caused by the fluid pressure inwerking chamber 46a which is varied by a solenoid-operated pressure selector valve 66. Valve includes a housing having an inletl port 67 connected with high pressureport t3 via conduit 68a, a

motor port o9 connectedy with the working chamber 46a'. Vvia conduit tib, and a pair of exhaust ports 7@ and'71 y connected with sump 45' via the branch'lines of conduit 72. A reciprocable valve plunger '73, provided with lands'74land 75 separated by groove 76controls communication between the valve housing ports. Anaxial passage 77, extending into plunger 73 and terminating in a pair of radial passages 7S, vents the chamber 8S at the left end oi the plunger bore. Plunger 73Vis biased to the right intofcontact with fixed stop 79 by coil spring 31 and, whenv the plunger 73 is in this position, inlet port 67 is closed by land 74 and spring seat working chamber 46a is connected with sump via conduit 68h,

Y port 69, groove '76, port 76 and conduit 72.

Secured to one end of plunger 'is the movable armature of a stationary solenoid coil do, the state of energization of `which is controlled by switchl. When this switch is open to deenergize the solenoid, plunger 73 assumes the position shown in FiG. 2. When solenoid S6 is energized by the closing of switch S7, armature 85 is moved Vto, the left by magnetic attraction to shift plunger 73 to the left against the bias of spring S1 to asecond position in which inlet port 67 communicates vwith outlet port 69 via groove 7d, and exhaust port 713 is closed by lan-d 75. This shift of plunger 73 permits pressure fluid from high pressure port d to-tlow to working chamber 46a where it is effective to move seat V59V into engagement with stop 65 and. thus increase the loadingrof spring 69. As a result, pilot valve dois caused to operate at its second reference pressure-establishingv condition.

Operation of cam stop motor 32' is controlled by a second solenoid-actuated valve 91. Thisvalve includes a housing having an inlet port 92 connected with high pressure port 8 via conduits 93 and 63a, a motor port 94 groove 1193. The plunger also` contains axial and radial passages 11M, and 1615, respectively, serving to vent the chamber 119 at the left end fof the plunger bore. Coil spring 106, mounted in the chamber 1111, biases plunger,V

99 to a first position (shown inFiG. 2) `in which land 101 ycloses inlet port 92 and groove 1tl3`interconnects ports 94 and 96. inthis position, working chamber 32a is connected with sump 45 via-conduit 95, port 9d, groove 1%, port 96 and conduit 9S. The plunger 99 is shifted t to the leftagainst the bias of spring 10d by yasolenoid whose coil 168 is connected with switch 109 and whose` armature is attached to the right end'of the valve plunger.

When switch 109 is closedto energize solenoid 1113, the

valve plunger is moved to ka positionrin which exhaust port 96 is closed by land 102 and inlet port 92 is connected with motor port 94 via groove 103. When valve plunger 99 is in this second position, pressure iluid is supplied from high pressure port 8 to the working chamber 32a of cam stop actuating motor 32 via conduit 68a, conduit 93, port 92, groove 103, port 94 and conduit 95.

During pumping operation of the hydraulic unit 3, luid is supplied to themain hydraulic system of the vehicle via conduit 111 containing valve 112 which is operable between closed and open positions.

OPERATION The operation of the hydraulic starting and pumping system may now be described. For the purposes of the following discussion, it will Ibe assumed that the constant pressure source 41 comprises a pressure compensated pump regulated to deliver fluid at a maximum pressure of 3200 p.s.i. and having a control range extending between 3100 and 3200 p.s.i. According to the invention, the maximum capacity of this pump (which will be assumed to be 30 gallons per minute) is less than the maximum capacity of the hydraulic unit at starter cut-out speed (assumed to be 50 gallons per minute). Assume also that a pressure of 200 p.s.i. is required in positioning motor working chamber 26a to position the cam plate in its maximum stroke-establishing motoring position against the bias of spring means 19, and that a pressure of 100 p.s.i. is required to maintain the cam plate in its zero stroke-establishing position. Finally it will .be assumed that the first and second reference pressure values established by pilot valve 46 are 2900 and 3900 p.s.i., respectively, for causing the hydraulic unit to provide pumping pressures of 3000 and 4000 p.s.i., respectively.

. l. Motoring operation Assuming that valves 44 and 112 are closed and switches 87 and 109 are open, the initialpreloading of spring 60 urges pilot valve plunger 52 to the left to vent positioning motor working chamber 26a via conduit 48h, passage 49, groove 57, passage 50 and conduit 51. Worleing chamber 46a behind spring seat 59 is vented to sump via conduit 68h, port 69, groove 76, port 70 and conduit 72, and Working chamber 32a of the cam stop operating motor 32 is vented to sump via conduit 95, port 94, groove 103, port 95 and conduit 93. Cam plate 15 is positioned in its maximum stroke-establishing pumping position by spring means 19, as shown in FIG. 1.

As soon as starter shutao valve 44 is opened, pressure fluid from constant pressure source 41 tiows to high pressurexport 8 through flow restrictor 43, valve 44 and con-` duit 42. The setting of tlow restrictor 43 is based upon the flow of fluid required to obtain full displacement motoring at the ignition speed (light-off in the case of a jet engine) of the internal combustion engine.

Since the pilot valve inlet passage 47 communicates with conduit 42 via conduit 48a, the fluid pressure in passage 47 increases to exert a force on the left-hand endy surfaces of lands 53 and 54 which displaces plunger 52 to the right against the bias of spring 60. Plunger 52 moves to the right until a lap position is reached in which land 54 interrupts communication between motor passage 49 `and exhaust passage 50 to discontinue venting to sump of the Working chamber 26a and spring chamber 62. The pressure required to hold plunger 52 in this lap position against the biasing force of spring 60 is the reference pressure against which the fluid pressure at high pressure port 8 is compared. Since spring seat 59 is in its FIG. 2 position, the rst reference pressure value of 2900 p.s.i. is established and when the pressure in inlet passage 47 exceeds this value, plunger 52. moves further to the right to interconnect inlet passage 47 with motor passage 49 through slots 58 and groove 56. Pressure uid is now transmitted to working chamber 26a through conduit 48h and to spring chamber 62 through radial and these two chambers rises to a value at which the sum of the force of spring 60 and the pressure force acting on the right end of plunger 52 exceeds the pressure force acting on the lett end of this plunger, the plunger 52 moves to the left toward its lap position. When it has again reached the lap position, the pressure established in Working chamber 26a and spring chamber 62 will be equal to the difference between the pressure of fluid at high pressure port 8 and the reference pressure. Further increases in pressure in conduit 42 produce equal in creases in pressure in Working chamber 2da and spring chamber 62.

As the pressure in inlet passage 47 progressively increases to 3200 p.s.i., the pressure in working chamber 26a progressively increases from zero to 300 p.s.i. and cam plate 15 is moved from its FIG. 1 position to its FIG. 2 position by the positioning motor 26. The pressure iluid applied from the source to high pressure port 8 is transmitted through the housing and valve plate passages to the cylinder barrel -bores 11 to urge the pistons 12 to the left in FIG. 2, and the pistons react with the inclined cam plate 15 to apply torque to the cylinder barrel to drive the hydraulic unit 3 as a motor. Since the cam plate 15 is at its maximum stroke-establishing motoring position, the hydraulic unit operates initially at maximum displacement to drive the power shaft of the internal combustiony engine 3S via mechanical connection 39.

For the purpose of the following discussion, starter cut-out speed is defined as being that speed of the motor at which the internal combustion engine is started and achieves independent operation, andl ignition speed is deiined as being the speed of the motor at which the engine is ignited (for example, light-ofi in the case of a jet engine). It will be assumed that ignition speed equals 60% of starter cut-out speed.

As the hydraulic unit accelerates during motoring operation, a progressively increasing iluid demand is made on the source. For example, as the hydraulic unit accelerates from zero to ignition speed, the demand on the fluid source 41 increases from Zero to 30gallons per minute. Since the source 41 is a pressure compensated pump (as for example, a hydraulic unit similar to that of the present invention when it is operated as a pump), the source automatically increases its capacity in an effort to maintain system pressure. However, when the demand of the hydraulic unit exceeds the 30 gallon per minute maximum capacity of the source 41, the source no longer can maintain system pressure and this pressure drops below the lower limit (3100 p.s.i.) of the control range of the source. According to the present invention, the pressure-res`ponsive displacement control means of the starter are now operable as a function of this decrease in system pressure (which occurs as the unit accelerates from 60% to full starter cut-out speed) for reducing unit displacement in an effort to maintain system pressure.

As the speed of the hydraulic unit increases further during motoring operation (for example, to y70% of starter cut-out speed), a greater quantity of hydraulic iluid is demanded by the hydraulic engine thanV is supplied through conduit 42 and the pressure drops momentarily at high pressure port 8. Assuming that the pressure at high pressure port 8 decreases to 3075 p.s.i., the pressure in conduit48a and in inlet passage 47 drops accordingly with the result that the pressures in spring chamber 62 and Working chamber 26a decrease to 175 p.s.i. Spring means 19 then pivots cam plate 15 slightly in the clockwise direction to reduce the displacement of the hydraulic unit to correspond to the rate of flow of uid in conduit 42. As the speed of the hydraulic engine increases further (for example, to of starter cut-out speed), the pressure at high pressure port 8 decreases (for example, to 3050 p.s.i.), the pressure in Working chamber 25a decreases to 150 p.s.i., and the cam plate 15 is displaced in the clockwise direction by spring means 19 to further reduce hydraulic unit displacement.` y

2. Pumping operation port` 8 to the spring seat working chamber '45a via conduit 63a, port, 67', groove 71,A port 69 andV conduit 68h; Spring seat Sttis displaced to the left against stop 65 to increase the preloading of spring 60' and thus establish the second reference pressure against which the;

pressure atV high pressure port 8 is compared. Plunger 52 is urged to the left by spring e0 to vent working chamber 2da and cam plate 15 is positioned at its maximum stroke-establishing position by the spring means 19. As the pressure at high pressure port 8 nowgincreases to 3900 p.s.i., the pressure in inlet chamber 47 increases correspondingly to move plunger 52 to itslap position.

After the internal combustion engine has. accelerated tothe point that it develops sucient power to drive the hydraulic unit as a pump, solenoid-'controlled valvel 4liis closed to isolate the system from the fluid source 41 and as'a result of the iiuid4 leakage which occurs in the hydraulic unit, `the pressure at high `'pressure port 8' momentarily drops slightly below 3000 p.s.i. and the cam plate is displaced slightly overcenter on the pumping side of neutral so that the hydraulic unit pumps sutiicient` iiuid to bring the pressure at high pressure port S up to the 3000 p.s.i. operating pressure. Closing of switch 109 causes plunger 09 to move to the left whereupon huid is applied to stop motor working chamber 32u from high pressure port 8 via conduit 68a, conduit 93, port 92,1 groove 103, port 9e and conduit95. Cam stop 34a is displaced to the lettl to prevent cam'plate 15 from moving in the counterclockwise direction from its natural position toward its maximum stroke-establishing motoring position.

Since the hydraulic unit is now being driven as a pump to supply iluid at a pressure of 3000 p.s.i. from port S, the pressure in inlet passage 47 is 3000 p.s.i. and the pressure in working chamber 26a is 100 p.s.i. and the cam plate is positioned in its zero stroke-establishingneutral position. vWhen valve 112 of the auxiliary hydraulic system supply line 111 is opened, a ow demand is created and the pressurek in inlet chamber 47 decreases- (for example, to 2990 p.s.i.). The pressure kin working chamber- 26a decreases to 90 p.s.i. and cam plate 15 is pivoted in the clockwise direction by spring means `19 to increase displacement of the hydraulic unit in an eiort to bring thei'system pressure up to 3.000 p.s.i. When the system rpressure is again returned to this operating pressure, canr plate 15 is returned to its zero stroke-establishing position by the positioning motor 26. If the system Vdemand increases further to reduce the pressure to 2900V p.s.i., the pressure in working chamber 26a decreases to zero and the cam plate is positioned in itsmaximum strokeestablishing pumping position. As the system pressure is brought up to 3000 p.s.i., the cam plate 15 is progressivelyV returned to its zero stroke-establishing position. In the eventy that a very large system demand is presented which causes system pressure to drop below the reference pressure value of 2900 p.s.i., plunger 52 is no longer malntained vin its lap position against the bias of spring 62,

and the spring urges plunger 52 to the FIG. 2 yposition to vent working chamber 26a. Cam plate 15 is maintained in its maximum stroke-establishing pumping position by spring means '19 and the hydraulic engine operates continuously at maximum displacement in an efort to bring the system pressure up to its operating value. When the system pressure increases above 2900 p.s.i., plunger 52 As the pressureat high pressureport 8- increases to 4000 p.s.i.,` the pressure in working chamber 26a increases to 100 p.s.i. to position cam plate 15 in its zero stroke-establishing position. If the system demand causes the pressure at high pressure port to decrease Vmomentarily (to 3990 p.s.i., vfor example), cam plate 15 'isr moved to the right slightly to increase displacement and to bring the system pressure back to 4000 p.s.i., at which time the cam plate is returned to its zero stroke-es-` tablishing position. Consequently, during pumping operation, the hydraulic unit operates as a pressure-compensated variable displacement pump tending to maintain kan operating pressure of 4000 p.s.i. when the control valve establishes a reference pressure of `3900 p.s.i. andV an operating pressure of 3000 p.s.i. when theV controly valve establishes a reference pressure of 2900 p.s.i.

In order to return Athe hydraulic unit 3 to motoring operation, switches Wand-109 are opened, Valve 112l is closed and solenoid-controlled valveV 44' is opened. The motoring and pumping operations are thenrepeated in the mannerdescribed above. l

It is important to note that although the flow restrictor 43 has been illustratedV and described as being arranged intermediate the source 41 and the solenoidcontrolled valve 44, the restrictor could be included equally as wellwithin the actual starter control system. Furthermore, a iiowk restrictor need beyprovided only when the capacity of the source-is greater than the demand of the motor-pump unit when it is operated as. a motor at a predetermined speed (i.e., at the ignition speed of the internal combustion engine) Vwhich is less than starter cut-out speed. In inherently( flow-limited systems using a source of limited capacity (i.e., a source which supplies fluid at a rate insuicient. to meet the demand of'the hydraulic motor at ignition speed ofthe internal combustion engine), the use of a ilow restrictork is not necessary to obtain the starter control operation of the present invention. However, from a .practical standpoint it appears desirable to incorporate the iiow restrictor even in inherently now-limited systems, since auxiliary fluid supplies are often used and since bench testingV of the starter system can be performedV more readily if the ow restrictor is an-integral part of the device.

While in accordance with the provisions ofthe patent statutes we have illustrated and described -the best form and embodiment of the invention now known to us, it will vbe apparent to-those skilled in the. art that other changes may be made in the apparatus described without deviating from the invention set forth in the following claims.

What is claimed is: f

l. A hydraulic starting system for accelerating an engineto starter cUt-outspeedcomprising v rit.

out speed and its displacement control element is in maximum displacement-establishing position;

(c) conduit means connected with the motor and the source for leading iluid from the source to and the displacement control element is in the maximum displacement-establishing position;

(c) conduit means connected with the motor and the source for leading uid from the source to and through the motor; and

(d) motor control means connected with the displacement control element and `responsive to the operating pressure of the motor for positioning said element in the maximum displacement-establishing position when operating pressure is above a predetermined value and for moving said element toward the minimum displacement-establishing position as the operating pressure tends to decrease below said predetermined value, whereby the change l@ -uiiit of the overcenter type having high and low pressure yports and a displacement control element movable between first and second maximum displace- `ment-establishing positions on opposite sides of a l through the motor; and zero displacement-establishing position; l

(d) motor control means, vindependent of the source, (b) a reservoir connected with the low pressure port; connected with the displacement control element (c) a source of hydraulic uid,including a variable and responsive to the flow demand lof lthe motor for delivery, discharge pressure compensated hydraulic positioning said element in the maximum displacepump, connected with the unit and capable of dement-establishing position when the motor is running 10 livering iluid at a substantially constant pressure and and the demand is below said maximum delivery at a rate that varies between a minimum value and rate and for moving said element toward the minia maXmemfValue equal te Ille demaud 0f the motormuni displacement-establishing position as the ilow Pump llllt When that unit 1s operating at a certain demand tends to increase above said maximum de- Speed leSS than C uf- Out Speed and the` displacement livery rate, .whereby the change in displacement of Y control element is in the rst maximum displace- .the motor maintains motor demand substantially merit-establishing position;l I Y f Y e constant at the rate of demand at isaid certain speed. (d a IS Shut-01T Valve for COHHCClDg ald dlSCOHIleC- 2. A hydraulic starting system for accelerating an 111g the Source and fille motor-Pump 111C engine to starter cut-out speed comprising (e) a delivery conduit connected with the high pres- (a) a variable displacement hydraulic motor having Sure PON;

a displacement control element movable between e Second Silutof Valvelocated 111 the dehVelY C011' minimum and maximum displacement-establisliing du fol' Openlng and Closing Salle; and positions; (g) control means connected with the displacement (b) a source of hydraulic fluid, including a variable control elemeflt and feS P 011S 1Ve t0 the Operatm Pres' delivery, discharge pressure compensated hydraulic Sure 0f the lm lt for POSltlOnm the dlSPlaCemeUt C011- pump, capable of delivering fluid at a substantially 'fmleement 1 I1 the TS maXlmUm d}SP1aCeme11t-e$ constant pressure and at a rate that varies between abhshljng POSIUOU When the Fre SSUfe 1S aPOVe a Pfee minimum Value and a maximum value equal to determined value and for moving the displacement the demand ef `the meter when the motor is meme control element'tolward the second maximum dising at a certain speed less than cnt out speed and placement-establishing position as the pressure tends to decrease below said predetermined value. 6. A hydraulic starting and pumping system as deiined in claim 5 including (a) stop means for preventing the displacement control element from moving from the zero displacementestablishing position toward the first maximum displacement-establishing position; and

(b) means connected with the stop means for selectively rendering it effective and inelfective.

7. A hydraulic starting and pumping system as defined in claim 5 in which the control means comprises (a) spring means biasing the displacement control element toward the second maximum displacement-establishing position;

(b) a iiuid pressure positioning motor connected with lagisprtrt afsgl lgunmailrgl de' 45 the displacement control element for moving said 3. A hydraulic starting system as defined in claim 2 ,sellllilgtirgoieast mammum dlsplacement-esl (ugs lgitlhthtg Isnginlsli the pump (c) a pilot valve responsive to the operating pressure (b) which includes ow limiting means interposed in of the unit for selectively pressurizing and venting the conduit means between the source and the motor for limiting the rate of supply to the motor to said maximum value.

4. A hydraulic starting system as dened in claim 3 in the positioning motor, respectively, as the pressure rises above and decreases below said predetermined value.

8. A hydraulic starting and pumping system as dened in claim 7 including selector means connected with the pilot valve for causing the pilot valve to pressurize and vent the positioning motor, respectively, as the pressure rises above and decreases below a pressure higher than said predetermined value.

9. The method of accelerating an engine to starter cutout speed using a variable displacement hydraulic motor comprising which the motor control means comprises (a) spring means biasing the displacement control element toward the minimum displacement-establishing position; (b) a iluid pressure positioning motor connected with the displacement control element for moving said element toward the maximum displacement-establishing position; and

(c) a pilot valve responsive to the operating pressure of the motor for pressurizing the positioning motor a certain amount sucient to cause it to move the dis- (a) generating fluid under pressure and supplying same to the motor to cause it to accelerate the engine; (b) maintaining supply pressure substantially constant L .e placement control element to the maximum displacehnlfnuis van d from a mmlmum Value ment position when the operating pressure is above c) operating the motor at maximum displacement Sald Pfedetermm Vdue and for reducmg, the Preis' until the engine accelerates to a certain speed less sure in the positioning motor below said certain than cnt out Speed. nllount thedoperamgdprelssure tends to decrease (d) starting the engine at least by the time it reaches e 0W S31 .Pre etrmme V? ue; said certain speed so that it commences to develop 5-. A hydraulic starting and pumping system for acceltorque; eralng an engine 'i0 Starter CUOP Speed and for Supply- (e) limiting the rate of supply of fluid to the motor to ing fluid under pressure comprlsing the rate demanded by the motor at said certain (a) a variable displacement hydraulic motor-pump speed; and

l l2 (f) thereafter reducing the displacement of the motor (d) starting the engine at least by'the time it reaches Y as the engine accelerates to Starter-eut-Out Speed t0 said certain speed so that it commences to developv thereby maintain the oW demand of the motor subtorque; i Y Stanlly'ons'fant at'he fate demanded by it at Said Y (e) limiting the rate of supply of uid to the motor to certamspeed'Y 5 the rate demanded by the motor. at said certain speed;

10. The method of accelerating an engine to starter cutf and out speed using a variable displacement hydraulic motor (f) thereafter reducing the displacement. ofy the motor i" comprising c 1 l Y f A e me to e rno or to cause 1t to acce era e t e en me; n .l Y i" (b) .regulating the rate of generation of ud under 10 constant at the rate demanded at said certain speed.

pressure in accordance with the demand of the motor v v to thereby maintain supply pressure substantially References Cited 1n therme of thls Patent constant; i UNITED STATES PATENTS Y Y (c) operating the motor Yat maximum displacement 15 2 838 908 Forster' v June, 17 1958 until the engine accelerates to a' certain speed less 

1. A HYDRAULIC STARTING SYSTEM FOR ACCELERATING AN ENGINE TO STARTER CUT-OUT SPEED COMPRISING (A) A VARIABLE DISPLACEMENT HYDRAULIC MOTOR HAVING A DISPLACEMENT CONTROL ELEMENT WHICH IS MOVABLE BETWEEN MINIMUM AND MAXIMUM DISPLACEMENT-ESTABLISHING POSITION; (B) A SOURCE OF HYDRAULIC FLUID CAPABLE OF DELIVERING FLUID AT A SUBSTANTIALLY CONSTANT PRESSURE AND AT A RATE WHICH VARIES BETWEEN A MINIMUM VALUE AND A MAXIMUM VALUE EQUAL TO THE DEMAND OF THE MOTOR WHEN IT IS RUNNING AT A CERTAIN SPEED LESS THAN CUTOUT SPEED AND ITS DISPLACEMENT CONTROL ELEMENT IS IN MAXIMUM DISPLACEMENT-ESTABLISHING POSITION; (C) CONDUIT MEANS CONNECTED WITH THE MOTOR AND THE SOURCE FOR LEADING FLUID FROM THE SOURCE TO AND THROUGH THE MOTOR; AND 